The present invention relates to a coordinate inputting sheet; more particularly the present invention relates to such a coordinate inputting sheet which is suitable for being incorporated into a so called digitizer for inputting hand written letters and/or graphics; and even more particularly the present invention relates to such a coordinate inputting sheet, which is suitable for being incorporated into a so called digitizer for inputting hand written letters and/or graphics into, for example, a computer system, and which is also suitable for designating an area that is to be copied in, for example, a photo copying machine.
The present inventors wish hereby to attract the attention of the examining authorities to copending patent application Ser. No. 056892, filed June 3, 1987, which may be considered to be material to the examination of the present patent application.
In the prior art, there have been proposed various types of coordinate inputting sheet for a digitizer for a computer system or the like. Such a prior art type coordinate inputting sheet is illustrated in FIG. 6 of the accompanying drawings in sectional view. In this figure, the reference symbol 61 denotes a X coordinate inputting sheet, which has a resistive surface on its lower side as seen in the figure, and which has a pair of electrodes, not particularly shown, laid along its opposite edges and in contact with opposite edges of said resistive surface. And, similarly, the reference symbol 62 denotes a Y coordinate inputting sheet, which has a similar resistive surface on its upper side as seen in the figure and a similar pair of electrodes, not particularly shown, laid along its opposite edges and in contact with opposite edges of said resistive surface. These two X and Y coordinate inputting sheets 61 and 62 are laid together in a mutually skew perpendicular relationship, although this feature is not particularly shown in this figure.
With such a coordinate inputting sheet, when a tip of a special pen touches the upper or outside surface of the X coordinate inputting sheet 61 and presses on it, while at the same time certain voltages are applied between the electrodes of the X coordinate inputting sheet 61 and also between the electrodes of the Y coordinate inputting sheet 62, then divided voltages will be produced respectively from said X coordinate inputting sheet 61 and said Y coordinate inputting sheet 62 as X and Y coordinate information.
Further, in order to prevent the resistive surfaces of the X coordinate inputting sheet 61 and of the Y coordinate inputting sheet 62 coming into contact with one another in the absence of pen pressure, a plurality of insulating projections 63 are typically provided between said resistive surfaces of the X coordinate inputting sheet 61 and of the Y coordinate inputting sheet 62, as shown in FIG. 6. When one or the other of the points on the upper surface of the X coordinate inputting sheet 61 which are designated in FIG. 6 as P1, P2, P3, P4, and P5 is pressed with the appropriate pressure pen, then this point may be determined according to the different resistivity entailed through the correspondingly induced contact areas R1, R2, R3, R4, and R5 of the resistive surfaces of the X coordinate inputting sheet 61 and of the Y coordinate inputting sheet 62 which are mutually contacted together, as shown in FIG. 7.
There is however a problem with such a prior art type coordinate inputting sheet, in that, when the point P1 on the upper surface of the X coordinate inputting sheet 61 corresponding to the dead center point of the insulating projection 63 is pressed, then this pressure is obstructed by said insulating projection 63, and a contact area R1 is induced between the resistive surfaces of the X coordinate inputting sheet 61 and of the Y coordinate inputting sheet 62, said contact area R1 naturally not being at the dead center point of the insulating projection 63. This will typically produce an erroneous reading from this coordinate inputting sheet, regarding the inputted coordinates of the pressure point. In such a case, the obtained X and Y coordinate information may well be incorrect.